1. Field of the Invention
The present invention generally relates to a fuel injected internal combustion engine. More specifically, the present invention relates to a fuel injected internal combustion engine with direct fuel injection into the combustion chamber and spark-ignition.
2. Background Information
An example of a fuel injected internal combustion engine with direct fuel injection into the combustion chamber and spark-ignition is disclosed in Japanese Laid-Open Patent Publication No. 11-82028. In this publication, a fuel injection valve is arranged in an upper part of a combustion chamber and a cavity is formed in the top of the piston. The fuel injection valve injects a fuel stream generally shaped as a hollow circular cone toward the cavity of the piston and a spark plug ignites the fuel-air mixture formed by the injected fuel.
The cavity has a generally cylindrical surrounding wall surface, a bottom surface that connects smoothly with the surrounding wall surface, and a central protrusion that is shaped generally like a circular cone and connects smoothly with the bottom surface. The bulk of the generally hollow circular cone shaped fuel stream injected toward the cavity strikes the surrounding wall, proceeds along the bottom surface, and rises upward while following the contour of the protrusion and converging toward the center. As a result, the fuel-air mixture is formed that is concentrated in the area surrounding the spark plug, which is positioned directly above the protrusion. This arrangement allows excellent laminar combustion to be achieved.
The so-called swirl injection valve is sometimes used to inject fuel in such a manner that the fuel stream has the shape of a circular cylinder. The swirl injection valve injects the fuel while imparting a rotating component to the fuel flow inside the injection vent. The rotating component rotates about the axis of the injection vent.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved direct fuel injection engine. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that with a swirl injection valve as mentioned above, the penetration of the fuel stream is generally weak in the fuel injection direction. Consequently, in order to allow the majority of the injected fuel to hit the surrounding wall surface of the cavity it is necessary to keep the gas flow inside the cylinder extremely small. This requirement greatly restricts the degree of design freedom when designing the engine.
Furthermore, it has been discovered that the shape of the fuel stream sprayed from a swirl injection valve changes greatly depending on the cylinder pressure at the time of injection. Consequently, if the fuel is injected during the compression stroke, the pressure inside the cylinder changes greatly depending on the position of the piston. Thus, depending on the injection timing, it may not be possible to maintain the desired hollow circular cone shape.
One object of the present invention is to solve the problems resulting from the use of a so-called swirl injection valve.
The present invention is basically attained by providing a direct fuel injection engine comprising a combustion chamber, a spark plug and a fuel injection valve. The combustion chamber has a piston movably mounted therein. The piston includes an upper wall having a cavity with a fuel stream directing surface. The spark plug has a spark discharge gap arranged to ignite a fuel-air mixture in the combustion chamber. The fuel injection valve includes a front edge portion with a plurality of injection vents arranged and configured to directly inject fuel into the combustion chamber against the fuel stream directing surface as a plurality of solid-core fuel streams that strike at non-perpendicular angles. Each of the injection vents includes a center spraying axis and a predetermined spraying angle. The adjacent pairs of the injection vents are further arranged such that the center spraying axes form predetermined separation angles between adjacent pairs of the solid-core fuel streams that are equal to or smaller than the spraying angles of the injection vents.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.